A rare earth magnet, which is represented by a neodymium magnet (Nd2Fe14B) and neodymium magnet films which apply to MEMS (Micro Electro Mechanical Systems), is used as a very strong permanent magnet having a high magnetic flux density for various applications. In order to further increase the magnetic coercive force, the crystal grain size is being reduced to the nano-scale (several tens to several hundreds of nm).
In typical sintered magnets (crystal grain size: several μm or more), as is known, a heat treatment is applied after sintering so as to increase the magnetic coercive force. For example, in Patent Documents 1 and 2, it is confirmed that the magnetic coercive force can be enhanced, when an aging heat treatment at a temperature of not more than the sintering temperature is applied.
However, it is unknown whether the above-described effect would be obtained in a magnet composed of nano-size crystal grains. That is, the fineness of the structure is considered to greatly contribute to the increase of magnetic coercive force, and therefore a heat treatment has not been performed because of the risk of coarsening the crystal grain.
In a rare earth magnet having a nanocrystalline structure, the enhancement of the magnetic coercive force by a heat treatment is desirable. Accordingly, it is needed to establish an optimal heat treatment method.